This invention relates generally to golf club heads and, more specifically, to faces for golf club heads that provide for improved performance and appearance. The invention also relates to methods of making such faces for golf club heads.
Golf clubs include a shaft and a head. The head generally includes a hosel, a face, a sole, and a back to form the hollow head. The face includes an exposed impact surface, upon which a golf ball impacts during a golfer""s swing. The impact surface, though typically smooth over most of its surface area, can incorporate a number of different markings. These markings can be ornamental and provide no substantial effect on ball movement, or they can be designed to affect the movement of a ball striking the impact surface. The main factor in determining whether a marking on the impact surface affects ball movement is its depth. Decorative sandblasting or fine milling, for example, generally produces markings on the impact surface having depth less than about 0.10 mm. Though these markings are visible, they do not substantially affect the movement of a ball.
Other markings on the impact surface are designed to affect ball movement. For example, grooves commonly are used on the impact surfaces of club faces. The particular dimensions of these grooves are determined by the United States Golf Association (U.S.G.A.), as described in Appendix II of the U.S.G.A. Rules. These grooves generally range in depth from at least about 0.15 mm to about 0.50 mm (the maximum allowed under U.S.G.A. rules), and they are placed on the impact surface to provide increased spin rates for balls hit off the face. Increased spin rate provides increased aerodynamic lift and improved controllability of golf balls hit off the impact surface. Other markings, such as round punch marks, also can be used on the impact surface.
The ball markings discussed above designed to affect ball movement also can be aesthetically appealing. Golfers are accustomed to seeing grooves or other markings on the impact surfaces of club faces, and they generally do not prefer a xe2x80x9cblankxe2x80x9d look on a large portion of the impact surface. Besides their aesthetic appeal and effects on ball movement, markings on the impact surface serve as guides to golfers for proper placement the club prior to striking a ball. A golfer who is in an xe2x80x9caddressxe2x80x9d position, in which he is preparing to hit a ball, looks down on the face at an angle generally parallel to the face. The golfer can use markings on the impact surface as landmarks, allowing for improved placement of his shot. Removing markings from the impact surface of the face removes this utility.
Despite the potential advantages above, use of deeper markings affecting ball movement, such as grooves, presents certain disadvantages. Because these markings cut more deeply into the impact surface of the face than the shallower decorative markings, the thickness of the face is substantially reduced at the markings. As a result, overall face thickness must be increased to maintain structural integrity of the face and prevent formation of stress fractures along the edges of the markings. This is particularly important for markings placed at the central region of the impact surface, because this region receives the greatest number of impacts, as well as impacts imparting the most force on the impact surface. Increasing the overall face thickness leads to a reduced coefficient of restitution (C.O.R.) for the club head, resulting in reduced ball speed and distance for balls hit using the head.
To prevent the need for thickening of the face, these deeper markings can be omitted from the impact surface, leaving only shallow decorative markings on the striking surface. This is particularly appropriate for driver heads that, as discussed above, do not require markings, such as grooves, to provide increased ball spin. However, use of these shallow markings alone provides for reduced utility of the markings, because they are difficult, if not impossible, to see at address when the golfer is viewing the impact surface at an angle generally parallel to the impact surface. The deeper markings are more clearly seen at address and provide superior guidance to a golfer.
In view of the above, there remains a need for a face for a golf club head that allows for high C.O.R. without formation of stress fractures on the impact surface of the face, while maintaining an appearance that is aesthetically appealing and serves as a guide to golfers. The present invention fulfills this need and provides related advantages.
The present invention is embodied in a face for a golf club head that has an impact surface incorporating a central region that includes the geometric center of the impact surface. The central region is free of markings having depth greater than about 0.10 mm. Shallow markings are located in the central region having depth less than about 0.10 mm. Deep markings having depth greater than about 0.15 mm are located outside the central region. Preferably, the central region covers at least about 10 percent of the impact surface, more preferably about 20 percent, and most preferably about 40 percent.
In preferred embodiments of the present invention, the central region is disc-shaped with its center at the geometric center of the impact surface, and it preferably has a radius of about 0.6 cm, more preferably about 1.0 cm, and most preferably about 1.5 cm. Preferably, the shallow markings have depth of at least about 0.01 mm, and more preferable they have depth of about 0.02 mm. The shallow markings may be regions of texture comprising indentations and extrusions from the plane of the impact surface, or they may be regions of oxidation of the impact surface.
The deep markings preferably have depth of less than about 0.50 mm, and most preferably they have a depth of about 0.20 mm. In a preferred embodiment, the deep markings are straight grooves having constant width and depth. These grooves may be horizontal, vertical, or combinations of these. The shallow markings preferably are elongated straight markings having a width similar to that of the grooves, and they preferably are substantially parallel to at least a portion of the grooves. Preferably, the shallow markings generally extend to the edges of the central region.
In a preferred embodiment of the present invention, the impact surface incorporates a heel region and a toe region, and the central region is situated between the heel region and the toe region. The heel region and the toe region each incorporate deep markings. Preferably, the impact region also incorporates at least one deep marking above the central region. Preferably, the deep markings are filled with paint.
The present invention also is embodied in a face for a golf club head incorporating an impact surface having: a circular central region extending from a geometric center of the impact surface having a radius of about 1.5 cm, and free of markings having depth greater than about 0.10 mm; a heel region and a toe region, such that the central region is situated between the heel region and the toe region; horizontal shallow markings located in the central region, the shallow markings being straight and having depth between about 0.01 mm and about 0.10 mm; and, horizontal grooves located in the heel region and the toe region, the grooves being straight and having depth between about 0.15 mm and about 0.5 mm and substantially constant width and depth. Preferably, the grooves are colinear with and have width similar to that of the shallow markings. The horizontal shallow markings preferably have depth of about 0.02 mm, and the horizontal grooves preferably have depth of about 0.20 mm. The impact surface preferably incorporates a horizontal framing groove above the central region that is straight and has a depth of about 0.20 mm. The impact surface also preferably incorporates a horizontal shallow marking outside and preferably below the central region, the shallow marking being straight and having depth of about 0.02 mm.
The present invention also is embodied in golf club heads having a hosel, a face, a sole, and a back, the face as described above. The golf club head preferably is incorporated into a driver or a fairway wood.
The present invention also resides in a face for a golf club head comprising an impact surface free incorporating the geometric center of the impact surface, wherein the central region is free of markings having depth sufficient to impart substantial spin to a ball striking the markings. Shallow markings having depth insufficient to impart substantial spin to a ball striking them are located in the central region. Deep markings having depth sufficient to impart substantial spin to a ball striking them are located outside the central region.
The present invention also resides in a method for making a face for a golf club head including the steps of: forming a face having an impact surface, the impact surface incorporating a central region free of markings having depth greater than about 0.10 mm; forming markings having depth between about 0.15 mm and about 0.50 mm on the impact surface outside the central region; and, using media blasting or laser energy to form markings in the central region having depth less than about 0.10 mm. A preferred aspect of the method includes the steps of: forming a face having an impact surface, the impact surface incorporating a toe end, a heel end, and a central region free of markings having depth greater than about 0.10 mm and situated between the toe and heel ends; forming toe grooves on the toe end and heel grooves on the heel end; placing a layer of removable coating material having openings in the layer over the impact surface, so that the openings overlay part of the central region; media blasting the layer for a duration such that shallow markings having depth less than about 0.1 mm are formed on the impact surface at the openings; and removing the layer. The method preferably includes filling the toe grooves and heel grooves with paint.
Other features and advantages of the present invention should become apparent from the following detailed description of the preferred embodiments.